1. Field of the Invention
The present invention relates to an elongated object including a cable surrounded by at least one external protection, and to a manufacturing method of said elongated object.
The elongated object can typically be used in subsea. More particularly, the elongated object is in contact with a heating pipeline, and the cable of said elongated object can be a subsea pipeline direct electric heating (DEH) cable.
2. Description of Related Art
For heating of oil or gas pipelines in order to prevent hydrate and ice formation on the pipeline walls, a DEH cable is installed to supply current to such heating system. Such DEH cable, so called “piggyback” cable, is traditionally laid on the pipeline. More specifically such a cable is strapped to the pipeline during installation thereof.
DEH cable is based on the fact that an electric alternating current (AC) in a metallic conductor generates heat. The heated pipeline is an active conductor in a single phase AC electrical circuit, together with a single core high voltage cable strapped to the pipeline.
DEH cable can typically contain one or several conductors surrounded concentrically and successively by a conductor screen, a cross-linked polyethylene insulation and an insulation screen. It cannot have any metallic material such as armouring outside the protective sheath, since it would make possible an undesired electrical path for return current, hence detracting from the effectiveness of the system. Thus, the cable is generally protected by an external plastic protection from damage which may be caused by outer impact forces such as by fishing gears or falling objects.
An example of external plastic protection for DEH cable fixed to a heating pipeline, is presented in the document EP 1 686 301. This document proposes an electrical cable wrapped with an external protection. The external protection comprises several different cross sections arranged end to end around the electrical cable. The joints between the sections are staggered.
As mentioned in said document, the sections are obtained from great lengths extruded elements, said elements being coiled on a reel. Said reel is transported to a vessel and the elements are cut off with a length of about 3 m to form said sections. Then, the sections are laid around the cable drawn-off from a cable drum.
In another installation embodiment, directly after the extrusion step, the extruded elements can be cut off with a 3 meter-length to form said sections. Thus, the sections are packed on pallets for delivery to a vessel in view of their installation around the cable.
In all the cases, several sections of about 3 m each are necessary to protect the whole length of the cable portion to be protected.
However, the sections are not so easy to install around the cable due to the different type of sections, the staggering between joints and especially the sections preparation including the cut off of the sections.
In the domain of umbilical cables as described in U.S. Pat. No. 5,813,106 or WO01/16515, the umbilical cable, which classically is a signal cable or a 3-phase cable, is composed of a plurality of elongated channel elements surrounding a steel tube. Said elongate channel elements are adapted to receive conduits and cables. They are obtained from extruded PVC profiles, and may have voids in the operational configuration of the umbilical cable.